1. Field of the Invention
The present invention relates to a trunk interface unit for use in a remote access system (RAS), and more particularly to a trunk interface unit for interfacing with a digital trunk of a public switched telephone network (PSTN) in the RAS for connecting the PSTN to a different network (for example, a packet network, Internet, etc.).
2. Description of the Prior Art
In general, a PSTN performs a circuit switching according to call requests from telephone subscribers to transmit voice signals to other subscribers on the network. A packet network is a communication network for sending digital data among computers by a packet switching. These networks can be integrated to a broadband integrated services digital network (B-ISDN). However, since the B-ISDN is composed of individual networks, a service exchanging, procedure among the networks is very complicate.
As is well-known, the PSTN is chiefly directed to telephone voice services. However, according as personal computers (PC) are widely used and various information providers (IP) using the packet network appear, a connection between the PSTN and the packet network is required. Accordingly, there is a need for the RAS for connecting the packet network to a domestic telephone line.
The RAS is connected to the PSTN by a T1 or E1 trunk and to the packet network by a protocol X.25. Conventionally, for the connection of the RAS to the PSTN, separated trunk interface units are needed according to the type of the trunk, that is, T1 or E1 trunk, and a block for transmitting subscribers' data and a block for performing an R2 signaling are separately provided. Therefore, the conventional trunk interface unit has a complicated circuit structure, thereby increasing its cost of production.